Nitrogen gas makes up 78% of Earth’s atmosphere and is an essential component in amino acids and proteins.

However, plants and animals cannot use nitrogen gas directly.

Plants can only absorb nitrogen in the form of nitrates.

Minerals

Nitrates and other minerals are taken into a plant via specially adapted root cells called root hair cells.

Cross section of a root hair. Labels showing Active transport (minerals in lower concentration in the soil than in cell cytoplasm) and Osmosis (Soil water is more dilute than root hair cell sap).

They are specially adapted by having a long extension that provides a large surface area for absorption.

Nitrates are absorbed by the process of active uptake/transport, which moves the mineral from an area of low concentration in the soil to an area of high concentration, against a concentration gradient, in the plant root.

Energy (from aerobic respiration) is required to move minerals against the concentration gradient so this process needs to happen in the presence of oxygen.

Plants use nitrates to make amino acids and proteins; these are then transferred to animals in the food chain.